4. Females: Ability to avoid pregnancy for at least 6 months after receiving the last study vaccination: Women physically capable of pregnancy (not sterilized and still menstruating or within 1 year of the last menses if menopausal) must have avoided pregnancy from 28 days prior to administration of the study vaccine and must have agreed to avoid pregnancy through at least 6 months after receiving the last study vaccination. Acceptable methods of avoiding pregnancy included a sterile sexual partner, sexual abstinence (not engaging in sexual intercourse), or use of a combination of at least two forms of acceptable contraception: hormonal contraceptives (oral, injection, transdermal patch, or implant), vaginal ring, intrauterine device (IUD), and the use of a condom or a diaphragm; or the use of a condom or a diaphragm combined with spermicide.